1. Field of the Invention
The present invention relates to a hybrid integrated circuit device with a power active filter mounted on an insulating metal substrate, and more particularly to a hybrid integrated circuit device in which malfunction of a small signal circuit caused by switching noise can be avoided and a leak current from the insulating metal substrate caused by switching actions can be reduced.
2. Description of the Background Arts
A switching regulator, called the active filter has recently attracted remarkable attention.
With reference to FIG. 10, the active filter is constituted of a bridge rectifier circuit consisting of diodes 60-66; a reactor 68 connected between an a.c. input terminal of the bridge rectifier circuit and an a.c. power terminal with a voltage represented by V.sub.ac ; a transistor 70 connected in parallel between a pair of d.c. output terminals of the bridge rectifier circuit; a control circuit 76 which normally outputs the control pulse .phi. of a frequency over 15 KH.sub.Z ; a condenser 74 for smoothing a d.c. output of the bridge rectifier circuit; and a dumper diode 72 connected between the d.c. output terminal and the smoothing condenser 74.
When the control pulse .phi. of the control circuit 76 is a high level to turn on the transistor 70 during the half-period while the polarity of a.c. power supply of the reactor 68 in the active filter is positive, a closed circuit is formed between the reactor 68, the diode 60, the transistor 70, and the diode 66. A current flows from the a.c. power supply to the reactor 68, where the energy is stored up. After that, when the control pulse .phi. is at a low level to turn off the transistor 70, the closed circuit is opened and a counter electromotive force is produced in the reactor 68 at the same phase as that of the a.c. power supply. The sum of the counter electromotive force and the voltage of the a.c. power supply is input into the bridge rectifier circuit consisting of the diodes 60-66, and then by the output from the bridge rectifier circuit, the dumper diode 72 is forward-biased to charge the smoothing condenser 74.
Conversely, if, during the half-period while the polarity of a.c. power supply of the reactor 68 is negative, the control pulse .phi. of the control circuit 76 is at a high level to turn on the transistor 70, a closed circuit is formed between the reactor 68, the diode 64, the transistor 70, and the diode 62. A current flows from the a.c. power supply to the reactor 68, where the energy is stored up. After that, when the control pulse .phi. of the control circuit 62 is a low level to turn off the transistor 70, in the same manner as above the sum of the counter electromotive force of the reactor 68 and the voltage of the a.c. power supply is input into the bridge rectifier circuit, and then the output from the bridge rectifier circuit causes the dumper diode 72 to be forward-biased, thereby charging the smoothing condenser 74.
As discussed above, because a high voltage, which is the sum of the counter electromotive force and the voltage of the a.c. power supply, is input into the bridge rectifier circuit of the active filter, continuous power supply to a load side is allowed. The active filter in comparison with ordinal switching regulators possesses the advantage of no switching actions at high voltages and currents. This type of active filter and a switching regulator used therein are, for example, disclosed in Japanese Patent Laid-open (Kokai) No. 150,972/1981.
Conventionally, the active filter is constituted of discrete parts. Switching regulators consisting of such discrete parts, however, requires lengthy wirings between the discrete parts, and thus it has the disadvantage of inducing a new noise caused by inductance components of the wires. This type of active filter must therefore be sealed within a large housing, and hence a demand for power devices of more decreased size has never been satisfied. In order to solve this problem, the present inventors have proposed in Japanese Patent Application No. 2580/1988 a hybrid integrated circuit device with an active filter mounted on an insulating metal substrate.
Referring to FIG. 11, this hybrid integrated circuit device is provided with a metal (for example, aluminum) substrate 80, and both surfaces of the substrate are coated with insulating oxide films 82 made by means of an anodic oxidation process. On one of the insulating oxide films 82, a conductive pattern 86 made from a copper foil is formed through an insulating resin layer 84 of, for example, epoxy Diodes 60-66 (not shown), a transistor 70, and other circuit elements for a control circuit 76 (not shown), which are all in a chip form, are mounted on the conductive pattern 86 to form the hybrid integrated circuit device. An excellently minimized active filter is thus realized. Additionally, as shown in FIG. 11, a ground pattern among the conductive pattern 86 is connected with the metal substrate 80 beneath the insulating oxide film 82 by a bonding wire 88 for purposes of removing floating capacitance caused by the insulating oxide film 82 and insulating resin layer 84.
Generally, incorporation of such hybrid integrated circuit device into electronic equipment is accomplished in a structure with excellent heat dissipation characteristics, that is, attaching to a chassis the insulating oxide film 82 on the other surface (the back surface) of the metal substrate 80. In this structure, however, the insulating oxide film 82 serves as a dielectric between the metal substrate 80 and the chassis of electronic equipment and as a result floating capacitance may arise on the entire surface of the metal substrate 80.
The hybrid integrated circuit device having the above structure was found to have a specific problem peculiar to the use of an insulating metal substrate. In other words, the potential at an emitter of the transistor 70 of the active filter largely fluctuates with high frequencies, leading to occurrence of noise in the chassis of electronic equipment.
Referring to FIGS. 12 and 13, the problem will be reasonably explained.
FIG. 12 shows an equivalent circuit for the hybrid integrated circuit device during the half-period while the polarity of power-a.c. current at the reactor 68 side is positive. During the positive-going half-period, the reactor 68, the diode 60, the transistor 70 and the diode 66 forms a closed circuit, and the reactor 68 serves as a collector load of the transistor 70.
Conversely, FIG. 13 shows an equivalent circuit for the hybrid integrated circuit device during the half-period while the polarity of power-a.c. current at the reactor 68 side is negative. During the negative-going half-period, the diode 62, the transistor 70, the diode 64, and the reactor 68 forms a closed circuit and the reactor 68 serves as an emitter load of the transistor 70.
As discussed above, during the positive-going half-period (see FIG. 12), the potential at the collector of the transistor varies as if it were switched with the frequency of control pulse .phi. between the charge potential of the smoothing condenser 74 and the ground potential. Here, the potential at the emitter is kept at the ground potential. On the other hand, during the negative-going half-period (see FIG. 13), the reactor 68 serves as the emitter load of the transistor 70, and hence the potential of the emitter varies as if it were switched with the frequency of control pulse .phi. between the charge potential of the smoothing condenser 74 and the ground potential.
Because the ground pattern of the hybrid integrated circuit device is connected with the aluminum substrate 80 by the bonding wire 88 as shown in FIG. 11, the potential at the aluminum substrate 80 varies as if it were switched with the frequency of control pulse .phi. between the charge potential of the smoothing condenser 74 and the ground potential during the negative-going half-period. These potential variations are delivered into the chassis of electronic equipment as a switching noise due to the effect of the floating capacitance C.sub.p produced between the aluminum substrate 80 and the chassis of electronic equipment.
In addition, in the hybrid integrated circuit device of this type, the switching noise produced in its main circuit enters a small signal circuit, for example, a control circuit for controlling the transistor 70, through the circuit patterns that are combined electrostatically or inductively. This may give an obstacle to the operation of the device.
Furthermore, with switching regulators of this type, accumulation and dissipation of energy in the reactor 68 are carried out in a limited time, and therefore the working speed of the active filter is determined by the inductance of the reactor 68 and hence high operation speed can not be achieved.